'96 850 A/C compressor over temp sensor/switch?

Where exactly is the A/C compressor over temp sensor/switch on a '96

850?

I've had the problem others have been complaining about:

A/C blows cold for 10-20 minutes but then starts blowing normal hot air.

Local Volvo mechanic said basically that it means the compressor is going bad and that it would cost about $400 to replace it with a used one. Since summer is almost over I told them I'd wait until next year.

However if it is just bad sensor, and is easy to by-pass, I want to give it a try now while it is still hot. I've read lots of posts about this, but I have no idea where this sensor is and how exactly to by pass it.

Is there anywhere on-line that has pictures of where in the engine bay it is located and what needs to be done?

Any help would be greatly appreciated, especially from any of you who have tried this yourselves. Did it work?

Thanks!

Reply to
Atif
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The AC system is not only used in the summer time, but quite a bit in the winter time as well. Every time you turn on your defrost you are also turning on the AC system. Defrost does not simply blow warm hot air on your windshield, it blows dehumidified warm air on your windshield. An imporoperly running AC system will drastically decrease your ability to maintain a "fog" free windshield in the colder months. Bypassing the switches are not a viable option either. By bypassing the low pressure or high temp you can increadibly damage a system. You could introduce air and water which will result in acid or you can blow out a condensor, evap, line or any other portion of the system. Did this tech put gauges on it? That's really the only way to tell what's causing the premature cycling of the system. A defective compressor will not allow it to run cold at all.

-Brian

Reply to
Brian V

Well thats the thing they basically made it sound like they know from experience that the compressor is bad. The owner of the shop even said something like: We've spent so much time in the past chasing this or that with the A/C's that it is easier and cheaper in the long run replace the compressor. It isn't the evap since it does blow cold.

Reply to
Atif

OK, the evap gets cold, that tells us 2 things...1, that the compressor is running and the valve plates internally should be OK (not that they are perfect but OK). 2, that the system is not under charged. If it was under charged it would not be getting cold at all.

That leads us to 2 common things that could cause the system to shut off;

1, High temp, could be caused by a blocked condensor, not in the refridgerant side but where the air passes thru or a bad condensor fan motor or controls (if it has one). 2, High ref charge which is always possible when someone that doesn't have the proper tools or training works on an AC system.

So before you pay the yokels to give you a used compressor bring it to a reputible repair shop and have the system check properly rather than the "we've seen so many of these that it's got the be the compressor" answer.

It could be something as simple as a 30$ fan switch.

If your in the Boston area I can recomend an awesome mechanic who does work on the side from his regular shop foreman job at a local stealership.

-Brian

Reply to
Brian V

I believe the issue is with the notorious compressor overtemp switch; there have been recent threads about it. The proper fix is usually to bypass it because it never seemed to do any good - just shut down perfectly healthy systems.

Mike

Reply to
Michael Pardee

Hi Mike,

I haven't seen the threads, just found the group actually. I did a few searches and see that they have removed this switch in newer models. Most everything I have found blames it on the gap of the clutch as opposed to being a "defective switch"...I can see that happening...little slippage generates a whole heck of a lot of heat which can transfer to the body of the compressor where the switch is located. I still stand by my previous replies though, only real way is to throw the gauges on, not simply replace the compressor.

-Brian

Reply to
Brian V

Michael - right I remember reading about this in the previous threads. Hence my original post asks WHERE is this overtemp switch and how exactly do I by pass it? From the old threads it seems like it should be easy to do, but I don't know even where in the engine bay to be looking, and what to be looking for, and what to unplug, replug, change etc...

That is the information I need...

-Atif

Reply to
Atif

Brian -

If I just by pass the overtemp switch, can anything really bad happen? As I see it in a worse case scenario the lack of a switch causes the compressor to really go bad...but I'm looking at replacing it anyways.

I occasionally do travel to Boston so if you have the name of a person please let me know.

You can email me at:

atif *AT* myrealbox.com

just put "VOLVO" in the subject title as I normally just delete all the email in that account without looking at it.

If the switch was take out in later models, it can't be all that important, can it?

-Atif

Reply to
Atif

Hi Atif,

I sent Dave (the mech) an email with your contact info.

As far as the switch, it's on the compressor body itself. It should be the only electrical part on the body. The clutch also has 2 wires going to it, but you'll easily be able to differentiate between the 2. Simply follow the sensor leads back to the connector,unplug it, fashion up a jumper, weather proof it and your done. What damage it can cause...well if the sytem is operating properly and it is simply a defective switch then nothing bad will happen. If it's not whats causing your AC to cycle then it'll continue to happen.

I'd still prefer to see gauges on it!

-Brian

Reply to
Brian V

No need for a jumper on my 94. It was wired like this:

CLUTCH--------->>------SWITCH------>>---------CAR

After disconnecting the switch, I had two connectors, male and female. I just let them do what comes naturally, and ended up with this:

CLUTCH--------->>---------CAR

Each connector had a plastic weather cover over it. I used one of them to protect it and keep them from becoming unplugged.

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Reply to
Doug Warner

OK, dig out my trusty old fits-anywhere Coolpix-950 and a trouble light, and...

  1. Overall view. The area of interest is in the circle, just below the alternator:
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    The switch connectors are plugged together and set in the clip tothe right to keep them out of the way. The clutch to harnessconnector pair fits in the clip to the left.
    formatting link
    's a VERY tight fit down here. 3. A shot of the back end of the compressor. The switch itself is notvisible, since it's near the bottom. This is just to show the switchwires and sleeve that covers them. Shot from the upper right of thecompressor, looking down:
    formatting link

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Reply to
Doug Warner

Crap. Quite likely, if it's very hot there it could be the clutch gap which is too large. You just need to remove the clutch pulley and remove the right number of shims to get it back to the right spacing.

Mine measured 1.2mm gap when it should be 0.3 to 0.6mm max. Works a treat now.

The only thing is that to get to this, I found I had to remove the engine ECU and box, the power steering pump, the alternator, all the bracketry etc.

David.

Reply to
David Taylor

The actual switch is at the bottom, behind the compressor, don't be mistaken by the object with wires that is on the top at the front.

David.

Reply to
David Taylor

I do not see any reason to put a used compressor on the vehicle. At least install a rebuilt unit. The cost of labor, recharging the system, etc. make the installation of a used unit which might fail the next day seem rather foolish. For example,

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lists a rebuilt compressor at about $350 for the part.

No way would I install a used compressor, assuming that it indeed need replacement.

John

Reply to
John Horner

Not at all. The clutch not engaging means that the AC isn't functioning period. There's nothing that's going to overheat in that state.

David.

Reply to
David Taylor

Right, I think he said "used" and meant "rebuilt" (as opposed to a brand new one). I don't think they would actually recommend putting a used part like that into the car. That is the sort of thing that I would grill them about if I o.k.'d the work...

Where did you get the rebuild, does it have any warranty, etc etc...

Thanks,

-Atif

Reply to
Atif

this doesn't sound bad....however...

This is the part that I'd be worried about since I really don't have that much experience working on cars...

Reply to
Atif

I'm going to try this tomorrow, thanks for the warning about the forearms...I'll be sure wear an old long sleeve shirt or something!

Reply to
Atif

WOW! This is *EXACTLY* what I needed! THANK YOU!

There is just NO WAY I would have been able to figure out where this stuff is and what I should be looking for without these pictures.

I'll try this either this afternoon or Monday morning and let you all know if it works. This weekend I've been driving around and sure enough it works great for like 10-15 minutes and then just starts blowing warm air. I've leaving this week for a long drive so if the A/C works the whole drive I'll be psyched!

Thanks again!

-Atif

Reply to
Atif

There's no real knowledge required for this to be honest, just patience, tools and rubber arms.

Nothing needs to be disconnected, just removed so it's just a time consuming unbolting job. I would be interested to know the labour price though because it took me about 3 to 4 hours to get it all off (first time) and a couple to get it back on again. Frustrating if you're paying servicing prices because the actual shim removal takes just a couple of minutes, it's getting to it that takes ages.

David.

Reply to
David Taylor

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